Field of the Invention
The present invention relates to a run flat tire.
Background Art
Run flat tire means a pneumatic tire that can run in a certain extent of distance even in the state that air pressure in a tire has reduced and reached 0 kPa by tire failure such as puncture. It is known to reinforce a side wall part by providing a side reinforcing rubber part on an inner surface of the side wall part as a technique for enabling run flat running in the state that an inner pressure has reduced as above.
High hardness compounded rubber composition is frequently used in a side reinforcing rubber part to suppress deformation of a tire during run flat running (for example, see JP-A-2007-070373). However, when hardness is increased, tensile product is decreased, and there is a problem that durability effect cannot be sufficiently exerted.
The inventors of the invention have obtained the finding that the above problem can be overcome by forming a side reinforcing rubber part using a rubber composition containing a mercaptobenzimidazole compound.
Benzimidazole compound has been used in the past as an age resister, and in recent years, an attempt has been made to achieve both low heat generation and abrasion resistance of a rubber composition by using the compound.
For example, JP-A-2011-089031 discloses a rubber composition using a reinforcing filler and a benzimidazole compound having a carboxyl group or the like in predetermined amounts, and a pneumatic tire using the composition in a tread part and/or a side wall part.
JP-A-2013-216753 discloses a method for manufacturing a rubber composition for a tire tread, containing at least one selected from an amine type age resister, a phenol type age resister, a secondary age resister and a quinoline type age resister, and 2-mercaptobenzimidazole and its zinc salt are described as examples of the secondary age resister.
However, any of those patent documents does not disclose that in a run flat tire, hardness is improved without decreasing tensile product by using a mcrcaptobenzimidazole compound, thereby improving run flat durability.